Diffusion bonding process

Abstract

A diffusion bonding process provides a metallurgical bond between at least two metallic bodies having either iron or nickel as a component, utilizing a cobalt base alloy diffusion bondable to the metallic bodies at a temperature below the liquidus of either body but sufficient to promote interdiffusion of the cobalt alloy and metallic bodies. The bodies and alloy are contacted and subjected to the bonding temperature, whereupon solid state diffusion bonding occurs, producing a metallurgical bond which has a strength equivalent to brazing.

Having thus described the invention, what is claimed is: 
     
       1. A method for solid state diffusion bonding at least two metallic bodies of dissimilar composition comprising: providing a metallic body having either iron or nickel as a component;   providing a powder metallurgy body composed of a mixture of metal powders including either iron or nickel as one of the metal powders, the mixture of powders being shaped compacted to final form and pre-sintered, the powder metallurgy body having a cobalt base alloy powder blended with the metal powders, the cobalt base alloy being of a composition which promotes solid state diffusion bonding at a temperature below the liquidus temperature of either body;   contacting the bodies with an interference fit; and,   heating the contacted bodies to the sintering temperature of the powder metallurgy body wherein the powder metallurgy body is sintered and solid state diffusion bonding occurs between the bodies at the surface sites where the cobalt base alloy randomly occurs, bonding the bodies together.   
     
     
       2. The method of claim 1 wherein the alloy is provided as a coating to the surface of one of the bodies. 
     
     
       3. The method of claim 1 wherein at least one metallic body is a powder metallurgic body composed of a compacted mixture of powder metallurgical components. 
     
     
       4. The method of claim 3 wherein the bodies are heated to a temperature sufficient to sinter the powder metallurgy body. 
     
     
       5. The method the claim 3 wherein the cobalt-based alloy is blended with the other powder metallurgical components in the powder metallurgy body, the cobalt-based alloy randomly occurring at the bonding surface. 
     
     
       6. The method of claim 5 wherein the powder metallurgy body contacts a dissimilar metallic body with a controlled interference fit of 0.0003-0.0064 cm. 
     
     
       7. The method of claim 1 wherein the cobalt-based alloy comprises 7.5-9.5% by weight chromium, 27.0-30.0% molybdenum, 2.2-3.0% silicon, a maximum of 3.0% nickel and iron, balance cobalt. 
     
     
       8. The method of claim 5 wherein the cobalt-based alloy comprises 1-15% by volume of said powder metallurgy body. 
     
     
       9. A method for solid state diffusion bonding at least two metallic bodies of dissimilar composition comprising: providing a first metallic body having either iron or nickel as a component; providing a second metallic body having either iron or nickel as a component;   coating at least one of the bodies with a cobalt base alloy having a composition which promotes solid state diffusion bonding at a temperature below the liquidus temperature of either body;   contacting the first and second bodies with an interference fit; and,   heating the bodies to a temperature below the liquidus temperature of either body wherein solid state diffusion bonding occurs between the bodies through the cobalt base alloy, bonding the bodies together.   
     
     
       10. The method of claim 9 wherein said cobalt-based alloy comprises 7.5-9.5% by weight chromium, 27.0-30.0% molybdenum, 2.2-3.0% silicon, a maximum of 3.0% nickel and iron, balance cobalt. 
     
     
       11. The method of claim 9 wherein said cobalt-based alloy comprises 1-15% by volume of said powder metallurgy body.